Sheet metal panels are commonly used as components of commercial roofing structures. An assembly of panels is fastened together to form a generally flat cover over a roof substrate which may comprise a framework of wood or metal joists, a plywood surface supported on an underlying framework of joists, poured concrete or the like.
One type of joint structure commonly used for sheet metal roofing panels is that used to assemble the traditional flat lock roof. A flat lock roof panel has edge sections folded back over the main section of the panel to form hemmed edges. The hems are left slightly open to permit hooked engagement with the oppositely facing hem of an adjacent panel to form a joint defined by the overlapping hem sections. The joints are soldered to provide a watertight seal. Although used consistently for many years, this type of joint structure has several problems. For example, the engaged hem sections, when considered in cross-section, comprise four layers of sheet metal material which must be thoroughly heated from above to create conditions wherein the molten solder will be drawn into the joint sufficiently to form a reliable watertight seal. The soldering portion of the assembly process is thus time consuming and skillfully demanding. Soldering problems also arise where the sheet metal panels are nailed or otherwise fastened to the underlying substrate since those punctures through the sheet metal material must be sealed against the influx of water. Furthermore, sealing the joint with solder results in a rigid connection between adjoining panels which cannot yield to the strenuous forces induced by thermal expansion and contraction, and which may in turn cause buckling of the sheet metal material or breakage of the soldered seal.
A different type of joint structure for sheet metal roofing panels which overcomes several disadvantages of a flat lock joint structure is known as a standing seam. A standing seam, as opposed to the primarily horizontal configuration of a flat lock joint, has a vertical orientation with respect to the joint panels. Generally speaking, a standing seam is formed by first bending the edge portions of the roof panels to form vertically extending edge portions and adjacent panels are positioned on the roof so that adjacent edge portions are abutted against one another. A crimping or seaming machine is then used to fold the top edge sections to one side of the edge portions to form an overlapping standing seam. Thus, the edge portions of the panels are seamed about their top edge sections and unseamed at their bottom vertically-extending web sections. To avoid nailing the panels to the roof substrate conventional cleats have been used. Cleats have a horizontal base secured to the roof structure and a vertically extending web which fits between the panel edge portions so that one panel's edge portion abuts one side of the web while the adjacent panel's edge portion abuts the other side of the web. The top edge section of the web is folded over on one side along with the top edge sections of the edge portions of the panels to form the standing seam. While the joint is strengthened by the folding of the edge sections and the seam is relatively rigid, the edge sections of the joint are not in substantial line-to-line or face-to-face contact. Spaces exist within the seam. However, a particular advantage which standing seams have over flat lock joints is the fact that a standing seam does not need to be soldered since the juncture between the folded panel edges, where water might otherwise enter, is spaced vertically above the horizontal roof surface across which water drainage will flow. Thus, the spaces within the seam are not significantly detrimental. On the other hand, this advantage is offset by the fact that a standing seam may yet fail to provide adequate protection against the influx of water under conditions wherein the buildup of ice and snow would reach the vertically spaced folded connection between the joint panels and possibly force the entry of water between the folded edges. For this reason, standing seams have heretofore been used only for roofs having at least a pitch of 1 to 4, which is about a 14 degree vertical angle, in order to insure that accumulated ice and snow would slide off of the roof before reaching the vertically spaced seam.
The prior art has recognized the inability of roofing systems to use standing seams to construct flat roofs. One system, marketed in Europe under the name System Fagersta and described in the patents incorporated by reference above, produces a standing seam which can be applied to flat roofs. Basically, this system uses special cleats as described in the '681 patent and continuously welds the top edge sections of the edge portions of abutting panels before folding the top edge sections over onto one side as described in the '319 patent. The weld is positioned within the seam. Water which enters the space between the vertical edge sections through the folded seam would be blocked from further entry into the roofing assembly by the welded seam. However, any breaks or defects in the weld would defeat the watertight integrity of the joint. Furthermore, water trapped between the joint panel sections could possibly cause cracks or other leaks in the welded seam when expanding upon freezing.
The prior art fails to provide a standing seam joint structure for sheet metal roofing panels which provides adequate protection against the influx of water without the need for seam welding of the joint panel sections or soldering of the standing seam if the standing seam is to be used for roofing assemblies having little or no pitch.